We must ensure that we don't fast forcefully. If we'll observe the natural cycle of body there's something called 'Mandala'.
Mandala means that our system goes through a cycle in every 40-48 days. In every cycle there're three days when our body can go on without food. If we're aware of the way in which our body functions, we'll come to know about these certain days.
These days may differ from person to person & mayn't be in equal spacing. For those who aren't aware of the functioning of their body can fast during Ekadashi- the 11th day after full moon & the new moon.
One can also opt for fruit diet if staying without having food isn't possible.
